The tablets were among a variety of imported products seized by New York City health officials last year in immigrant-rich neighborhoods filled with exotic world goods -- some of which make it onto shelves without being evaluated by safety agencies such as the Food and Drug Administration.

Other products that have been the subject of recent warnings include two pesticides banned in the United States because they are dangerous to children: an Asian roach killer nicknamed "Chinese Chalk" and a Latin American rat poison called "Tres Pasitos," or "three little steps," referring to how far a rat can walk before succumbing to the poison.

Last spring, authorities urged residents to stay away from unpasteurized Mexican cheese that had turned up at groceries in Brooklyn and Queens, saying it may contain a bacterium that causes tuberculosis.

A surge in foreign imports has made it increasingly challenging for U.S. food, health and customs authorities to check the safety of all the products entering the country. About 13.7 million imported products subject to FDA regulation entered the United States in fiscal 2005, compared with 7.9 million three years earlier, the agency said.

Almost all shipments are subject to automated screening, during which computers hunt cargo invoices for products with potential safety problems. But only about 75,000 shipments each year wind up being sampled and tested, FDA spokesman Michael Herndon said.

Customs authorities get regular alerts on unsafe foods, cosmetics and medicines that should be barred, and inspectors seize items every week that don't meet U.S. standards, including contaminated fish from Asia and Mexican cosmetics with unsafe color additives.

But the system is less effective when it comes to undocumented cargo that crosses the border daily in trucks, people's luggage or car trunks, by mail or inside larger shipments.

The flow of those undocumented products is small, but it can add up in the nation's immigrant gateways.

California, for example, has struggled for years with the sale of imported Mexican candies contaminated with lead.

A small percentage of the shipments crossing the border are detected, and immigrants who grew up on the treats have been skeptical of claims that they could be dangerous, said Leticia Ayala of the San Diego-based Environmental Health Coalition.

"What we found out was that the FDA didn't have the capacity to deal with this huge issue," Ayala said. "Most of the things that come across the border aren't being tested."

A new California law now imposes a fine for selling contaminated candy, but authorities have yet to determine how much lead will trigger the penalty.

In New York, the city health department has cracked down on sales of skin creams and soaps from the Caribbean, Hong Kong and China that contained poisonous levels of mercury.

In January, it released a survey showing that the dangerous roach killer from Asia and rat poison from Latin America were still widely used in the city. A month earlier, a similar caution was issued about the Indian pills, Maha Sudarshan, and two other imported Indian herbal medicines with dangerous levels of mercury or lead.

Each had appeared on store shelves for some time before authorities realized they existed and could be a problem, health officials said.